1. Field of the Invention
The present invention relates to an overhead projector, more particularly to an overhead projector in which an original material can be retained stably on a stage.
2. The Prior Art
An overhead projector has a stage or working surface, and a projector head, which is arranged above the stage and incorporates a projector lens and a mirror. The stage supports an original material, namely a transparency on which opaque images are written or drawn. When the original material is placed on the stage, the image thereof is projected by the projector head onto a remote screen as an enlargement.
There are known two types of overhead projectors differing in position of the light source: the reflection type and the light transmission type. The light source of the reflection type is arranged in a unit incorporating the projector head, and the stage has a Fresnel mirror that supports the original material. On the other hand, the light source of the light transmission type is arranged beneath the stage, on which a Fresnel lens is placed to support the original material.
In conventional overhead projectors, original material to be projected is simply placed on the stage. If the original material is rolled beforehand, a problem has arisen in that the original material does not lie flat on the stage, due to the tendency of the original material to curl. The original material must be manually held, and kept flat and in contact with the stage, before images can be projected.
Furthermore, the original material may be slippery; and when the projector is so positioned that the stage slants, the original material has to be manually held to be kept from slipping along the stage.